1. Field of the Invention
The present invention relates to a disk drive device, in particular, to a disk drive device in which its anti-vibration characteristic is improved while reducing a drive current.
2. Description of the Related Art
In recent years, disk drive devices, such as Hard Disk Drives (HDDs), have been developed to be small in size and large in capacity, and been widely used in many electrical appliances. Therefore, disk drive devices have been used in a wide variety of environments. In particular, disk drive devices are being mounted in portable devices called mobile devices. Mobile devices are frequently used in environments with a lot of vibrations, and therefore the disk drive devices to be mounted in the mobile devices are demanded to have a characteristic in which read/write of data can be stably performed even when used in an environment with a lot of vibrations. In order to meet such a demand, there is a disk drive device in which a fluid dynamic bearing unit is mounted in which high-speed rotation can be stably performed. For example, Japanese Patent Application Publication No. 2007-198555 discloses an example of the structure of a fluid dynamic bearing unit, in which a flange forming part of a rotating body is arranged in the space between a sleeve forming part of a stator and a housing. By structuring a fluid dynamic bearing with the spaces between the flange and the sleeve and between the flange and the housing being filled with lubricant, smooth high-speed rotation of the rotating body is realized.
Because it is considered to be important that mobile devices are small in size, batteries for the mobile devices are often made small with the miniaturization of the mobile devices. As a result, it is often demanded that a drive current should be reduced when a disk drive device is to be mounted in a mobile device. If a drive current for a disk drive device is reduced, the dynamic pressure generated by a fluid dynamic bearing unit is decreased accordingly, resulting in a decrease in the stiffness of the fluid dynamic bearing unit. If the stiffness of a fluid dynamic bearing unit is decreased, a displacement in the axial direction of a rotating body including a recording disk becomes large when the disk drive device has vibrated. If a displacement of a recording disk becomes large, the relative distance between the recording disk and a magnetic head becomes unstable, thereby causing the problem that an increase in errors in reading/writing data may be incurred.